Large-eddy simulation of atmospheric convection on Mars

Large-eddy simulations are performed using the Mars Regional Atmospheric Modeling System (a non-hydrostatic, mesoscale model) in order to obtain a detailed, three-dimensional understanding of the daytime Mars atmospheric boundary layer. These microscale runs utilize the full radiative-transfer (including a static dust profile) routines of the mesoscale model and a multi-level, prognostic subsurface thermal model. Surface albedo, thermal inertia, Coriolis parameter and solar forcing are homogeneously set to values at the Mars Pathfinder landing site (19.33degreesN, 33.55degreesW (IAU1991); L-S = 143degrees). The initial state is obtained from a previous mesoscale simulation, and is representative of the Mars Pathfinder landing site during summer. The convective boundary layer of Mars is found to exhibit structures and turbulent statistics outwardly similar to those of earth's convective boundary layer. However, direct infrared radiative heating of the near-surface atmosphere is the primary mechanism for the transfer of energy from the solar-heated surface, and affects the behaviour of the convection. Mars convection is more intense than that on earth, primarily due to lesser gravity and atmospheric mass. Also, certain empirical scaling constants within the subgrid-scale turbulence parametrization (originally developed for terrestrial large-eddy simulations) appear to require significant reduction in order for the scheme to perform adequately on Mars. The simulation results are used to further meaningfully interpret spacecraft images of convective clouds. The results also compare favourably with Mars Pathfinder in situ meteorological measurements, and help reconcile large daytime variances in that dataset.